Self interest is present and given in economics. Self interest is the number one reason for doing anything in economics or in politics. Greed is a little stronger than self interest but still within bounds in the world we live in. Self interest and greed do not disappear when tasks are given to government and taken out of the free market realm. As a matter of fact greed and self interest are naturally kept in balance in a free market setting because exchange is voluntary. Competition keeps buyers and sellers from exploiting one another. When government takes over a task, there are no natural checks on greed and self interest. In free markets, self interest is a motive to economize. In Socialism self interest is a disincentive to economize so that inefficiency is the result.
Self interest and greed are never a problem in a free market system until laws are broken to achieve economic goals or until government is used as a tool to rig markets. Free markets cease to exist when government does not guarantee a level playing field. Currently, regulators are allowing laws to be broken right and left and government is constantly used as a tool to rig markets. Those are the source of today’s economic problems, not the existence of self interest and greed.